The present invention relates to a twin two-circuit pressure control unit with a change-over point which is adjustable from the outside. The pressure control unit serves motor vehicle dual hydraulic brake systems and has two cylinders, each of which are connections in a different one of the two brake circuits. The two cylinders are arranged parallel with respect to each other, and house the control pistons whose actuating pins project outwards from the same end of the cylinders and are acted upon by a common control lever. This control lever, is acted upon by a control force and which at the housing is supported tiltable around an axis which runs vertically with respect to the axis of the cylinders which means being provided for an even distribution of the control force to the two control pistons.
A two-circuit pressure control unit of this type is known from British Pat. No. 1,531,803 wherein, via the actuating pins, the control lever pushes the two control pistons into an end position in which the valves provided in the pistons are open. Above the change-over point defined by the piston surfaces and the force at the control lever, the control pistons will move outwards, forcing the control lever backwards, whereupon the valves provided in the control pistons will close, the pressure in the outlet chambers remaining unchanged. Thus, this known twin arrangement is a pressure limiter.
As the control force at the control lever increases the change-over point of the twin braking force control unit will change over to ever increasing pressures. This effect may e.g. be utilized for the purpose of increasing the control pressure in correspondence with the load of the vehicle and of thus increasing the braking pressures in the wheel cylinders in correspondence with the load. In the known braking force control unit the lever which is movable dependent on the state of loading is tiltable supported at the control unit housing by means of a pivot bearing. At the lever, a force transmission element is fixed which acts upon the control pistons and whose elastic design enables it, up to a certain extent, to permit an even pressurization of the two control pistons. The force transmission element connected between the actuating pins of the control pistons and the lever of the known prior art, however, is complicated as far as its manufacture is concerned and even implies additional tolerances and adjusting problems. As far as mass production is concerned, it is a disadvantage that assembly and positioning of the force transmission element at the lever require several operations which involve a lot of time.
Additionally, a pressure control unit is known which operates with but one stepped piston (German Patent DE-OS No. 2,706,785) wherein the control lever which it tiltable around a lateral axis acts on a single control piston.